Lasers, particularly solid state lasers, have been used for years for recording and reading or sensing data on optical media. It has also been found that the control circuitry, as well as the laser itself, are subjected to unintended changes in their operating parameters. Further, the operating parameters of media also vary from one medium to the next; such variation are significant when using so-called removable optical media.
It is, of course, common practice to calibrate the laser circuits to operate with a given optical medium; such calibration usually involves analyzing the laser light intensity at the optical medium, then setting operation of the laser control circuits to match a predetermined or desired light intensity at the optical medium. Such controls have been used to enable setting digital to analog converters (DAC) for enabling recording, writing, and erasing operations of optical medium. It is desired to provide a better control for such lasers in that the laser will be first calibrated for its own circuits for determining the power level changes of the digital analog converter steps such that a microprocessor can send a number to the digital analog converter to obtain a desired power.
Laser operations have been controlled independently of the optical medium. For example, in the Howard U.S. Pat. No. 4,709,369 those establishing a DC voltage which represent the peak value of light pulses out of a laser diode independent of the modulation pattern of the light pulses. Howard shows an integrative feedback loop which compares the desired power of the laser with the actual output from the conditioning means to establish an output current to cause the laser diode to supply light pulses of the desired value. Such conditioning includes a sample and hold circuit operative in association with an integrator feedback loop to perform at a rate as if the modulated or chopped light from the laser diode were continuously on. The adjustment of the laser is made by human operator. It is desired to eliminate the need for a human operator by automatically calibrating and adjusting the laser output.
The Ida, et al. U.S. Pat. No. 4,503,467 shows a digital to analog converter driven by an increasing counter for increasing the digital to analog converter output in a step-wise manner from a lower-limit value to an upper-limit value. Comparators compare the output signals of the light receiving units which are in a row of light receiving units with an analog reference signal which represents darkness or no light. Memories receive the digital signal and are controlled by the comparators to store instantaneous digital values when the corresponding comparators change their states i.e., capture the numerical value used to generate a predetermined analog value. It is desired to provide for a faster calibration technique not involving the use of digitized numerical values until after the calibration has been completed.